There has conventionally been known measurement of transmission characteristics of a device under test in the terahertz region.
For example, there has been known a device which measures transmission characteristics of a device under test using terahertz light modulated by an intensity modulation according to FIG. 1 of International Publication WO2003/005002. Terahertz light having a carrier frequency (f2−f1) and side band frequencies (f2−f1±fIF) is made incident to a device under test. As a result, the effective spectrum width (referred to as “incident spectrum width” hereinafter) of the terahertz light incident to the device under test becomes twice (2×fIF) as wide as that of the modulation frequency fIF.
However, according to the prior art described above, the frequency resolution of the transmission characteristics of the device under test decreases. The wider the incident spectrum width becomes, the lower the frequency resolution of the measurement of the transmission characteristics of the device under test becomes.
If the modulation frequency fIF is then decreased in order to increase the frequency resolution, the measurement accuracy for measuring the group delay time of the device under test (group delay resolution) decreases.
In this way, it is not possible for the prior art as described above to increase both the frequency resolution and the group delay resolution at the same time.
An object of the present invention is to increase the frequency resolution for measuring the transmission characteristics of a device under test.